“情态动词：许可与义务” （Modals: permission and obligation）
🔒 登录后可标记已读- 「可以做」「不准做」「必须做」「不必做」，这四种意思英文各有一套情态动词，用错一个意思就完全反过来。
- 许可用 can（日常）、could（更礼貌地请求）、may（最正式）。
- 禁止用 can't（规则上不准）和 must not/mustn't（强调禁令，公告常见）。
- 义务分两种来源：have to 是外部规定，must 是说话者自己的强烈义务感；must 没有过去式，过去要改用 had to。
- don't have to 跟 mustn't 完全是两回事——前者是不强制，后者是禁止，混用是最常见的错误。
重点内容
许可（Permission）
can — 最常用，日常口语请求或给予许可
- Can I sit here? → 我可以坐这里吗？
- You can use my car if you like. → 你可以借我的车。
could — 比 can 更有礼貌，用来请求许可（不用来给予许可）
- Could I ask you something? → 我可以问你一件事吗？
- Could I borrow your pen for a moment, please? → 我可以借一下你的笔吗？
may — 最正式，书面语、正式场合请求或给予许可
- May I see your passport, please? → 请出示您的护照。
- Customers may request a refund within 30 days. → 顾客可以在 30 天内申请退款。
禁止（Prohibition）
can't — 规则上不准（通常是外部规定，不是说话者自己制定的）
- We can't park here. → 我们不可以在这里停车。
- You can't take photos in the museum. → 博物馆里不可以拍照。
must not / mustn't — 强调禁令
- 用在公告、告示、法规上：
Visitors must not park in the staff car park. → 访客不得停在员工停车场。 - 说话者本人发出禁止时：
You mustn't be late to class. → 你不可以上课迟到。（老师对学生说）
义务（Obligation）
have to — 来自外部的规定，别人要求你做的
- We have to wear a uniform when we're working in reception. → 接待时我们必须穿制服。
- Al has to work tomorrow so he can't come. → Al 明天要上班，所以来不了。
- 过去式用
had to：I had to pay £85 to renew my passport. → 我不得不付 85 英镑续签护照。
must — 说话者自己的强烈义务感，或权威方的要求
- I must phone my dad. It's his birthday today. → 我必须给爸爸打电话，今天是他生日。
- Seat belts must be worn by all passengers. → 所有乘客必须系好安全带。
📌 must 没有过去式，表示过去的义务要改用 had to。
无义务（No obligation）
don't have to — 不强制，可做可不做
- You don't have to wear a tie. → 不用打领带（但你想打也行）。
- You don't have to go to the bank. You can do it online. → 不需要亲自去银行，网上也可以办。
📌 注意区分：mustn't（不准做）vs don't have to（不强制，不是不能做）
例句练习
| 英文 | 中文 |
|---|---|
| Could I use your phone? Mine's run out of battery. | 我可以用一下你的手机吗？我的没电了。 |
| You must hand in your homework by Friday. | 你必须在星期五之前交功课。 |
| You don't have to come early. The event starts at 8. | 不需要来太早，活动 8 点才开始。 |
| Guests must not smoke in the rooms. | 住客不得在房间内吸烟。 |
| I had to take a taxi because I missed the last bus. | 我不得不搭计程车，因为我错过了最后一班巴士。 |
常见错误
❌ You don't have to smoke here. (意思变成「你不强制要吸烟」) ✅ You mustn't smoke here. (你不可以在这里吸烟) （don't have to ≠ mustn't，前者是「不强制」，后者是「禁止」）
❌ I must went to the dentist yesterday. ✅ I had to go to the dentist yesterday. （must 没有过去式，表示过去的义务用 had to）
❌ Could I to borrow your pen? ✅ Could I borrow your pen? （情态动词后接原形动词，不加 to）
Sources
Blog / Website：